The present invention relates to a gear train.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
A gear train of a type involved here includes a housing and a shaft mounted therein. A gear wheel is attached to a first shaft shoulder, for example in the form of a spur gear, via a press fit, a groove-spring connection or the like. A first axial lock and a second axial lock are provided on the shaft to axially secure the gear wheel and accommodate the gear wheel between them. The first axial lock can, for example be formed, by a second shaft shoulder, the diameter of which is greater than the diameter of the first shaft shoulder receiving the gear wheel. A so-called groove nut is mostly used as the second axial lock, and is screwed onto the second shaft shoulder and presses against the gear wheel. German Industrial Standard DIN 981 distinguishes different designs of such groove nuts. A radial-axial slide-contact bearing unit is attached to a third shaft shoulder adjacent to but spaced apart from the second axial lock to radially and axially mount the shaft. The axial sliding-contact bearing of this radial-axial sliding-contact bearing unit requires running surfaces on both sides.
FIG. 1 shows a partial sectional view of a conventional gear train 1, which has a housing 2 and a shaft 3 arranged in the housing 2. Attached by a press fit to a shaft shoulder 4, which has a diameter D1, is a gear wheel 5, which in this case is a spur gear. Two axial locks 6, 8 are provided for axially securing the gear wheel 5. The first axial lock 6 forms a shaft shoulder 7 with a diameter D4 which is greater than the diameter D1 of the shaft shoulder 4. The second axial lock 8 is a standard commercially available groove nut 9 which is screwed to a shaft shoulder 10 arranged adjacent to the shaft shoulder 4. The gear train 1 includes a radial-axial sliding-contact bearing unit 11 which mounts the shaft 3 in the housing 2 and is attached to a shaft shoulder 12 provided adjacent to the shaft shoulder 10. The shaft shoulder 12 has a diameter D3 which is smaller than the diameter D2 of the shaft shoulder 10. The radial-axial sliding-contact bearing unit 11 has an annular recess 13 that extends originating from its internal diameter, which enables the radial-axial sliding-contact bearing unit 11 to be slid over the groove nut 9 such that the end surface of the gear wheel 5 facing the radial-axial sliding-contact bearing unit 11 forms a running surface 14 for the axial sliding-contact bearing of the radial-axial sliding-contact bearing unit 11. The other running surface 15 is formed by an axial bearing support disk 16 which is attached to the end of the shaft 3. The axial bearing support disk 16 has an annular and axially projecting shoulder 17 which abuts the end face of the radial-axial sliding-contact bearing unit 11 facing away from the gear wheel 5 and forms the running surface 15. The housing 2 has a housing cover 18 attached thereto, which positions the radial-axial sliding-contact bearing unit 11 against a housing shoulder 19 in a direction of the gear wheel 5. The housing cover 18 is provided with an annular, axially projecting protrusion 20 which positions against the radially outer region of the radial-axial sliding-contact bearing unit 11.
The design of the gear train 1 has shortcomings because the manufacture of the radial-axial sliding-contact bearing unit 11 is expensive as a consequence of the need for the annular recess 13. Furthermore, the annular recess 13 also entails larger dimensions than comparable radial-axial sliding-contact bearing units without such a recess. This is in many cases not desirable.
FIG. 2 shows a partial sectional view of another conventional gear train 10 which differs from the gear train 1 according to FIG. 1 by the absence of an annular recess in the radial-axial sliding-contact bearing unit 11 and by the presence of a further support disk 21 which is slid onto the shaft shoulder 12. The support disk 21 abuts the confronting end face of the shaft shoulder 10 and forms the running surface 14 for the axial slide-contact bearing of the radial-axial sliding-contact bearing unit 11 on the end face of the radial-axial sliding-contact bearing unit 11. The remaining structure corresponds to that of gear train 1.
The design of the gear train 10 has also shortcomings because of the need for the support disk 21 as an additional element that has to be manufactured and fitted. This renders the design complex and increases costs.
It would therefore be desirable and advantageous to provide an improved drive train to obviate prior art shortcomings.